There are many instances where the flow of a liquid medium through relatively small diameter pliable plastic tubing systems is regulated by the incorporation in the tubing system of a flow control or metering device of comparatively small size and light in weight so that the device is capable of being supported or suspended in place in the tubing system solely by the tubing itself. In the medical field, for example, such type flow control or metering devices are commonly employed to regulate the flow of medical fluids through intravascular catheter systems which customarily employ elastically deformable or compressible plastic tubing such as that commercially known as Tygon tubing and which are conventionally used for various medical purposes such as, for example, blood dialysis, clinical monitoring of a patient's blood system, or infusion of various medical fluids into a patient's venous system.
The flow control or metering devices heretofore employed for such purposes generally have been of complicated construction difficult to fabricate and/or assemble. With such prior flow control or metering devices, moreover, and more particularly those employed for regulating the flow of medical fluids to a certain number of drops thereof per given time interval, the adjustment or setting of the device to the desired minimal flow rate for the medical fluid thrcugh the device generally has been a difficult and critical operation to perform involving in most cases an undesirable time consuming trial and error procedure.
The prior type metering devices, moreover, generally have not been provided with any visible indicator means or any so-called memory device affording a ready indication of the adjusted setting of the metering device that provided the desired flow rate of the liquid medium through the device. As a result, when such prior metering devices were moved to a closed position for some reason or other so as to close off the flow of the liquid medium through the tubing system, for instance, to check the reason for a stoppage of the liquid flow through the tubing system, it then became necessary to manually readjust the setting of the device, generally by trial and error procedure, in order to restore the previous setting of the device so as to provide the same rate of flow of the liquid medium through the tubing as before. Obviously, such a resetting procedure constitutes a time consuming operation and therefore an undesirable characteristic of the prior type fluid flow metering devices such as used for medical purposes.